The present invention relates to valves having adjustable seats and, more particularly, to damper valves having seats which are variably adjustable.
Damper valves of the butterfly type are known in which a blade, usually of circular shape, is mounted for pivoting between an open position and a closed position to control the flow of fluid through the valve. A shaft about which the blade pivots is positioned diametrically with respect to the blade and is mounted for pivoting in bearings beyond the periphery of the blade. A curved blade seat is positioned in a valve body for side, that is, axial, engagement with one of the faces of the blade along the periphery of the blade.
The blade, the seat and the body can all be made of stainless steel and can be fabricated with precision. However, during handling, shipment and installation of the valves, the body can deform slightly, especially since the valves are large, typically having a diameter of several feet. Even a slight distortion, for example, on the order of less than 0.0001 inch, can have an adverse effect on the sealing ability of the valve.
The problem of loss of precise seating due to deformation of the body or other parts of the valve was overcome by the valve disclosed in U.S. Pat. No. 5,494,257 issued to the present inventor. More particularly, that patent discloses a valve with an arrangement for adjusting the seat along the length thereof to ensure a tight seal despite variations that might take place in the valve during shipping or installation, or at other times. The valve can be used with fluids at relatively high temperatures, for example, 800.degree. F.
The arrangement of that valve includes a fixed seat member mounted on an inner surface of a valve body or base and having a side surface positioned for axial engagement with an overlapping portion of a side surface at the perimeter of the valve disk or blade. A portion of the seat on one side of the shaft is positioned on a first side of the blade, and a portion of the seat on the opposite side of the shaft is positioned on the frame for engagement with a second side of the blade. For each portion of the seat, an adjustable seat member is mounted on a surface of the fixed seat member facing the center of the frame, the adjustable seat member being movable axially relative to the fixed seat member, toward the valve blade, so that the adjustable seat member can be moved into engagement with any portion of the valve blade where the fixed seat member does not contact the blade. Bolts are provided at spaced locations along the lengths of the fixed valve seat member to secure the adjustable seat member to the fixed valve seat member when the desired precise positioning of the adjustable valve seat member has been achieved. A plurality of adjustment devices are spaced along the length of the seat and engage the adjustable seat members. Each adjustment device includes a threaded member, such as a bolt, engaging the adjustable seat member to move the adjustable seat member into sealing engagement with the blade at the needed places around the perimeter of the blade.
However, even with the improvements, there is a gas leakage through the valve which is more than an acceptable rate of leakage for some valve applications. As a result, it has been known to place two damper valves in series, each with its own blade and valve seat, in order to lower gas leakage to an acceptable level. In addition to greatly increasing cost, this practice greatly increases the space required for the installation of the valves in the conduit carrying the fluid to be controlled.